Heating at 40-41 C turns off RNA and protein synthesis and induces stage-specific developmental defects in Drosophila pupae. These defects can be prevented by a lower temperature (35 C) pretreatment which induces heat shock gene expression but does not shut off normal protein synthesis. Because of their resemblance to mutant phenotypes the heat induced defects are called phenocopies. Phenocopies probably result from interruption of gene expression during critical periods in development when gene expression is changing rapidly. Heating also causes birth defects in mammals including humans. Recently it has been shown that the molecular response to heat is similar in Drosophila and humans. This indicates that information about the molecular basis of the effects of heat on gene expression and morphogenesis in Drosophila will be applicable to higher organisms. We propose to use Drosophila as a system for studying the molecular basis for genetic and environmentally induced developmental defects. Preliminary results with the multiple wing hair mutant and phenocopy suggest that this defect may be caused by a change in timing of cell movement. We propose to use recombinant DNA technology and antibodies to identify gene products synthesized by mutants and wild type Drosophila during the normal development of wings and muscles and to follow expression of these genes under conditions which induce development defects.